高入射能量下的金属二次电子发射模型

基于高入射能量电子产生二次电子发射的物理过程, 分别对高入射能量电子产生的真二次电子和背散射电子的概率进行理论分析与建模. 利用Bethe能量损失模型和内二次电子逸出概率分布, 推导出高入射能量电子产生有效真二次电子发射的系数与入射能量的关系式; 根据高入射能量电子在材料内部被吸收的规律, 推导出高入射能量电子产生背散射电子的系数与入射能量之间的关系式. 结合两者得到高入射能量下金属的二次电子发射模型. 利用该模型计算得到典型金属材料Au, Ag, Cu, Al的二次电子发射系数, 理论计算结果与采用Casino软件模拟金属内部散射过程得到的数值模拟结果相符. 关键词： 二次电子发射 高入射能量 金属表面 散射过程     

Electron density and electron redistribution in alloys—I: Electron density in elemental metals

The changes in electronic structure around each metal atom in an alloy are more accurately described in terms of electron redistribution than electron transfer. The important elements in a model for such electron redistribution are the electron configuration and radius of the positive ion cores and the conduction electron density and its variation in the interstitial regions. Positive ion core radii for metals are derived from an empirical relation between ion core radii and intermetallic distance with electronic configurations of the core from positron annihilation data. These derived ion core radii are in good agreement with those calculated for metal electron densities by Welch and Lynn from Hartree-Fock wave functions. Average conduction electron densities can be directly calculated from these radii and the experimental atomic volume; the variation of conduction electron density in the interstitial region is calculated by assigning electrons to octahedral and tetrahedral interstices according to the Interstitial Electron Model. The calculated electron densities and the interstitial variation agree very well with the experimental electron densities of Be as determined from X-ray diffraction data as well as with calculated electron densities for Na, Mg and Al. Ion core configurations are compared with those derived from band theory and also those of the Engle-Brewer Correlation and the Samsonov-Pryadkov-Pryadkov Configurational Model.     

Quantum electron self-interaction in a strong laser field

The quantum state of an electron in a strong laser field is altered if the interaction of the electron with its own electromagnetic field is taken into account. Starting from the Schwinger-Dirac equation, we determine the states of an electron in a plane-wave field with inclusion, at leading order, of its electromagnetic self-interaction. On the one hand, the electron states show a pure quantum contribution to the electron quasimomentum, conceptually different from the conventional classical one arising from the quiver motion of the electron. On the other hand, the electron self-interaction induces a distinct dynamics of the electron spin, whose effects are shown to be measurable in principle with available technology.     

Electron dynamics and harmonics radiation due to electron oscillation driven by laser standing wave

The electron dynamics and harmonics radiation spectra due to electron oscillation driven by laser standing wave (SW) have been investigated considering a single electron mode. It is found that electron can pass through or be reflected from laser SW as electron is shot into laser SW from antinodes plane with initial velocity parallel to electric field of SW, and for electron incidence at arbitrary plane the attraction plane of electron trajectories will transfer from nodes plane to antinodes plane if initial electron kinetic energy exceeds a critical value. Further, the harmonics emission due to electron oscillation during passing through laser SW is considered in two cases of electron incidence plane at nodes and antinodes. In case of electron incidence at nodes, the spectrum of radiation is redshifted for backward radiation and blueshifted for forward radiation, and broadening of spectrum is noticed. These effects are much more pronounced at higher laser intensities. However, for case with electron incidence at antinodes, these phenomena vanish.     

129Xeq+轰击N型和P型Si表面时的电子发射产额研究

在兰州重离子加速器国家实验室测量了1.8 MeV Xeq+离子分别轰击N型和P型Si两种靶材表面时的电子发射产额。实验中,通过改变入射离子的电荷态,研究了入射离子势能沉积对两种靶材表面电子发射产额的贡献。结果发现同一离子入射时,N型Si表面的电子发射产额高出P型Si表面的电子发射产额约12.5%;对于具有相同入射动能的Xeq+离子,两种靶材表面的电子发射产额均随着入射离子势能的增加而线性增加。此外,还测量了3.4 MeV Xeq+离子分别轰击以上两种靶材时的电子发射产额,得到了类似的结果。本文利用功函数分别从动能电子发射和势能电子发射两个角度对实验结果进行了分析讨论。The electron emissions from N-type Si and P-type Si induced by 1.8 MeV 129Xeq+are measured in the National Laboratory of Heavy Ion Research Facility in Lanzhou,The contribution to electron emission yield from potential energy of incident ions is studied through changing the charge state of incident ions.The results show that for the same incident ion,electron emission yield of N type Si surface is higher than that of P-type Si surface about 12.5%.For incident ions with the same kinetic energy,both electron emission yields of two targets increase linearly with incident ion energy.In addition,the electron emissions induced by 3.4 MeV 129Xeq+from N-type Si and P-type Si mentioned above are measured,which give similar results.The experimental results are analyzed and discussed using work function from two angles of the kinetic electron emission and the potential energy electron emission.     

Electron temperature fluctuation in the HT-7 Tokamak plasma observed by electron cyclotron emission imaging

The fluctuation of the electron temperature has been measured by using the electron cyclotron emission imaging in the Hefei Tokamak-7 (HT-7) plasma. The electron temperature fluctuation with a broadband spectrum shows that it propagates in the electron diamagnetic drift direction, and the mean poloidal wave-number $\bar{k}_{\theta}$is calculated to be about 1.58 cm^-1, or \bar{k}_θ ρ_s≈ 0.34. It indicates that the fluctuation should come from the electron drift wave turbulence. The linear global scaling of the electron temperature fluctuation with the gradient of electron temperature is consistent with the mixing length scale qualitatively. Evolution of spectrum of the fluctuation during the sawtooth oscillation phases is investigated, and the fluctuation is found to increase with the gradient of electron temperature increasing during most phases of the sawtooth oscillation. The results indicate that the electron temperature gradient is probably the driver of the fluctuation enhancement. The steady heat flux driven by electron temperature fluctuation is estimated and compared with the results from power balance estimation.     

Study on electron emission suppression characteristic of molybdenum grid coated with Hf film by ion beam assisted deposition

Hf was deposited onto the surface of molybdenum grids by ion beam assisted deposition (IBAD). The electron emission characteristics from molybdenum grids with and without Hf, which were contaminated by active electron emission substances (Ba, BaO) of the cathode, were measured using an analogous diode method. The results show that electron emission from the grid coated with Hf film was less than that from molybdenum grid without Hf. The mechanism for electron emission suppression of the grids coated with Hf film was discussed.     

High density measurements of the Stark broadened profile of the He(II)4686 Å line

The Stark broadened profile of the He(II)4686 Å line has been scanned in the electron density range of 1–3 × 10¹⁸ cm^-3. The electron temperature, as determined from the line to continuum ratio, ranged from 9.4 to 19.9 eV. The plasma which emitted the He(II)4686 Å line was created in a 60-kJ theta pinch operated with a high fill pressure (3 and 5 torr) of pure helium. Electron densities were calculated from the half-half widths of the He(II)4686 Å line using two Stark broadening theories. These electron densities are compared with the electron densities determined from the absolute value of the continuum intensity and a total sweep up compressional model. The two theoretical models predict electron densities in good agreement with the electron densities from the absolute value of the continuum intensity.     

高速H2+离子轰击C靶诱发二次电子的发射行为与入射角的关系

运用Monte-Carlo方法结合半经验理论研究了高速H2+离子轰击C靶诱发二次电子的发射行为与入射角的关系。分别研究了电子发射产额与入射角以及发射统计性与入射角的关系。结果表明，由于H2+上的价电子的影响使得背向电子发射产额不遵守余弦倒数关系。斜入射时候的前向与背向电子产额的比值跟正入射时的情况不同。电子的发射统计跟入射角没有关系。标志偏离Poission分布的值 b，随入射能量的增加而增大。     

超热电子能量分布的实验和模拟研究

 采用LiF探测器堆测量了飞秒激光-薄膜靶相互作用中超热电子产生的剂量。根据电子在LiF中的质量碰撞阻止本领,理论上计算出了超热电子的能量分布;在相同实验条件下,数值模拟结果与实验测量结果较好地一致,证明了实验测量的可靠性。理论分析显示,共振吸收是激光-薄膜靶相互作用中电子加速的主要机制。     

Oblique Electron Thermal Waves in a Magnetized Plasma

Propagations of an oblique electron thermal mode under the electron plasma frequency without boundary effects are investigated experimentally and theoretically in a magnetized plasma. The phase, ray, and group velocity surfaces of the electron thermal mode are obtained in a polar coordinate. The experimental observation of the electron mode radiated from a point source is found to be in fair accord with the theoretical wave fronts which are obtained from the ray velocity surface. Wave fronts and ray trajectories of an oblique electron thermal mode radiated from a point source are numerically obtained in an inhomogeneous magnetized plasma with a use of an electrostatic kinetic theory. The spatial numerical results are indicated mainly below the electron plasma and cyclotron frequencies. Reflections of the mode in the plasma density lower than the electron plasma frequency are made clear numerically.     

微波大气击穿阈值的理论研究

本文通过对使用有效场强(或均方根场强)得到的微波大气击穿阈值表达式进行讨论, 指出其推导中所做的假设及这些假设应用到微波大气击穿过程中存在的问题. 然后分别使用解析理论和数值模拟对微波大气击穿过程中的有效电子温度变化过程和击穿阈值进行研究, 并将其与直流电场进行比较. 分析发现在高气压下, 电子能量转移频率高, 有效电子温度随电场大幅振荡, 由于电离频率随有效电子温度的增长率大于电子能量损失随有效电子温度的增长率, 因此在高气压时, 微波大气击穿阈值低于使用有效场强的击穿阈值. 通过大量分析, 给出了理论推导和数值模拟得到的微波大气击穿阈值拟合表达式.     

Investigation of the Anode Boundary Layer of an Atmospheric Pressure Argon Arc

This paper is concerned with the thermodynamic state of the plasma in the anode region of a high intensity arc. Spectrometric studies of the boundary layer in front of a plane anode perpendicular to the axis of a wall-stablized, high-intensity arc in argon atmosphere indicate substantial deviations from LTE. Data taken at distances of 0.5 to 2 mm from the anode surface are evaluated with two different but not entirely independent non-equilibrium data reduction techniques in order to obtain radial distributions of electron temperature and electron density. The electron temperature distribution displays an off-axis peak which increases in magnitude with decreasing distance from the anode. Both electron temperatures and electron densities are considerably higher than the corresponding LTE values.     

Atomic antenna: Nonlinear scattering of a superatomic-intensity laser pulse

A semiclassical model of high harmonic generation upon ionization by suppressing the atomic barrier is developed. The spreading of the wave packet of an ionized electron, which is chosen in the form of a Gaussian distribution, is considered. The quantum nature of the process is taken into account by the initial discrete level of the electron, and the finite wave packet spreading occurs in the continuum. After its detachment from the atom, the electron is assumed to be free and moving under the action of the laser pulse field and the Coulomb interaction of the electron with the atomic core can be treated as a perturbation. The radiation from the electron is calculated from its acceleration expressed in terms of the average force of interaction of the electron with the Coulomb center of the atom.     

Peculiarities of electron exchange between a negative hydrogen ion and atomic chains

This paper is dedicated to studying electron exchange between a negative hydrogen ion and an atomic chain with subsequent electron transport along the linear chain of hydrogen atoms. This process occurs after the electron transition from the negative hydrogen atom to the atomic chain. In our calculations, a method of wave packet propagation not using perturbation theory was applied. It is shown that the effectiveness of electron transport decreases uniformly as the distance from the ion to the chain increases. The electron propagates along the chain uniformly; in this case, the electron velocity is almost independent of the ion-chain distance.     

金属二次电子发射系数表达式

根据二次电子发射的主要物理过程,推导出二次电子发射系数和单位背散射电子产生的内二次电子数与原电子产生的内二次电子数之比、原电子入射能量、参数、最大二次电子发射系数、背散射系数之间的关系式。根据实验结果,给出了2~10 keV比率的表达式。根据推导的关系式,用实验数据分别计算出6种金属的平均参数。发现6种金属的平均参数都近似为一个常数11.89(eV)0.5。根据推导的关系式和计算的参数,推导出以背散射系数、原电子入射能量和最大二次电子发射系数为变量的二次电子发射系数通式。用该通式计算出二次电子发射系数,并与相应的实验值进行了比较,最后成功地推导出金属2~10 keV的二次电子发射系数通式。     

电子束空间极限电流的非线性理论研究

从电子束一维稳态传输的电势非线性Poisson方程出发,推导了圆柱波导内实心束和环形束空间极限电流与电子入射电势的依赖关系,给出了数值求解方法和解的特征,分析比较了数值计算与现有解析公式及粒子模拟的结果.考虑电子的横向运动,对数值方法进行了二维修正,计算结果与粒子模拟结果具有很好的一致性.说明利用数值方法计算电子电势非线性微分方程能够得到更精确的电子束在圆柱波导内的空间极限电流;另外,对其他形状的波导,尤其是难以得到解析式的情况,根据实际几何结构设置边界条件,数值方法可以方便地给出束流传输特性,对设计新型结构的高功率微波器件提供理论指导. 关键词： 相对论电子束 圆柱波导 空间极限电流 束流传输     

Experimental Study of Planar Langmuir Probe Characteristics in Electron Current-Carrying Magnetized Plasma

Experimental study of planar Langmuir probe characteristics in a magnetized plasma with an electron current along the direction of the magnetic field shows that the usual procedure for determination of the electron temperature and plasma density, which is applicable in a current-free magnetized plasma, gives erroneous results for these plasma parameters. When this procedure is applied on the characteristics measured at two opposite orientations of the probe collecting surface with respect to the direction of the electron drift, different values of the electron temperature are obtained. These virtual electron temperatures and corresponding plasma densities calculated from the measured ion saturation currents are higher and/or smaller than the exact local electron temperature and plasma density. Calculation of particular averages of these quantities is proposed as a possible way to obtain correct results for the local electron temperature and plasma density. These averages are used in the approximate evaluation of the electron drift velocity from the electron saturation currents measured at the two orientations of the probe collecting surface.     

Study of the relationship between coronal mass ejections and energetic electrons in interplanetary space

We consider time characteristics of energetic electron events in the interplanetary space after solar flares associated with coronal mass ejections (CME). Analysis of electron intensity-time profiles shows that independently of flare duration, times to electron event maximum from flare onset and from electron event onset increase with increasing of CME velocity. A possible interpretation of this effect is electron acceleration by CME associated with a shock wave.Published from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 1, pp. 46–52, January, 1996.This work was supported by the Russian Foundation for Fundamental Research (grant 94-02-04453) and by a Contract with EOARD (grant SPC-94-4071).     

近玻尔速度Ne2+离子穿过碳膜引起的电子发射

本文测量了入射能为2–25 keV/u的Ne²⁺离子穿过不同厚度碳膜诱导的前向、后向 (分别对应出射表面和入射表面) 电子发射产额. 实验中通过改变炮弹离子的能量, 系统的研究了势能沉积、电子能损以及反冲原子对前向、后向电子发射产额的贡献. 结果表明, 离子的势能沉积只对后向电子发射有贡献, 前向、后向电子发射产额分别与Ne²⁺离子在薄膜出射、入射表面的电子能损近似成正比关系, 其中电子能损很低 (对应于离子能量很低) 的时候, 反冲原子对电子发射的贡献不能忽略. 关键词： 近玻尔速度 电子发射 电子能损 反冲原子